Reuse existing implementations

With the component initializer mechanism it's possible to join existing client-side validation mechanisms of existing component libs (if client-side validation is supported).

An available solution is the Trinidad Support of ExtVal. It joins the client-side validation mechanism of Trinidad based on annotations.

Custom implementations

Furthermore, it's possible to implement a custom RendererInterceptor to build a custom client-side validation infrastructure.

(You will find very simplified demos for property- as well as bean-validation at http://code.google.com/p/os890/source/browse/#svn/trunk. Please don't use the demo as final solution. It just illustrates the required steps to get custom client-side validation up and running. So far there is no implementation you can use as final solution.)